1. Field of the Invention
This invention relates in general to means for converting electromagnetic waves having a given polarization into those having circular polarization by using a single or multi-layer conductor grid structure placed in front of the radiation aperture of an antenna.
2. Description of the Prior Art
Radar apparatus often is constructed with its tracking antenna adapted for linear polarization because with linear polarization under normal conditions the greatest range can be achieved. However, with a linearly polarized antenna, it is not possible to distinguish rain cloud echo signals which have a particular spectral distribution that is similar to actual moving target echo signals from real actual moving target echo signals. When using circular polarization on the other hand, rain cloud echo signals are strongly attenuated and distinguishing between actual moving targets and rain clouds can be easily accomplished. Therefore, in many instances the linear polarization of an antenna is converted into circular polarization for example by means of a polarization grid placed in front of the radiation aperture which are polarization grid is customarily integrated in the radome structure. Such known circularization grids are described for example in U.S. Pat. No. 3,754,271 and such grid is planar in shape.
A planar circular polarized grid of this type, however, frequently cannot be installed in existing radome in front of a radiation aperture because the available space does not allow such installation.